Stent

ABSTRACT

A stent ( 1 ) formed into a generally or substantially tubular body and expandable radially outward from inside of the tubular body, wherein cells ( 6 ) are connected vertically and so arranged as to surround the central axis (C 1 ) of the stent ( 1 ) and thereby to form annular units ( 4 ), the annular units ( 4 ) are extended along the axis of the stent ( 1 ), adjacent annular units ( 4 ) are connected at least at one portion by a connecting part ( 5 ), each of the cells ( 6 ) has at least one bent portion, and the angle of the bent portion after expansion of the tubular body until the diameter becomes 2.5 mm is larger than 30°. The stent ensures a high flexibility and radial support force, enhances the blood vessel expandability, and suppresses the foreshortening phenomenon and the flare phenomenon.

This application claims priority of International Application No.PCT/JP01/03368 filed on Apr. 19, 2001.

TECHNICAL FIELD

The present invention relates to improvement of a stent used to improvea narrowed portion caused in a living body such as a blood vessel andthe like.

TECHNICAL BACKGROUND

A stent is a tubular medical implement which is detained in the narrowedportion in question to ensure a required tubular region(space) byexpanding the narrowed portion and the like when a tubular portion of aliving body such as a blood vessel or other portions gets narrowed orclogged from obliteration. The stent is inserted into the body, with thediameter thereof small, and allowed to expand in the narrowed portion tomake the diameter thereof large so that the tubular portion in questionis expanded and kept in the expanded state.

The conventional stents, which are typically shown in FIGS. 11A, 11B andFIGS. 12A, 12B have the following problems. Incidentally, FIG. 11A andFIG. 12A are plan views showing the stents before expansion and FIG. 11Band FIG. 12B are plan views showing the stents after expansion.

In a stent 201 shown in FIG. 11A, a cell 206 constructing an annularunit 204 has a construction in which three straight line portions 207are connected in parallel, and a curved portion 206A between each cell206 is disposed opposite to the space 206B in the vicinity of anothercell 206 constructing another annular unit 204. Because of such aconstruction, the stent has an appropriate radial support force (namely,as shown in FIG. 11B, a force to maintain an expansion state of thestent against the outer pressure in the direction from the blood vesselwall, when the stent is expanded and fixed on the blood vessel wall) andan excellent flexibility. On expanding or delivering of the stent, sincethe stent is inserted, moving along a curved line at a bent portion ofthe blood vessel, a portion of the cell 206 is sometimes jutted out andcaught, which makes the delivery difficult (hereinafter, this isreferred to as a flare phenomenon).

Meanwhile, in a stent 241 shown in FIG. 12A, cells 246 constructing anannular unit 244 have a construction in which approximately orsubstantially<shaped strut (a striate body) 247 is connected by aconnecting part 245. Accordingly, it has the advantages that the stentis strong in radial support force, the approximately orsubstantially<shaped strut 247 never warps outward during expansion ofthe stent or when the stent passes through the bent portion of the bloodvessel, and so on. However, it has a problem of shortage of flexibility.This is because there is only one bent portion in the connecting part245 and the length of the connecting part 245 is short, as shown in FIG.12A.

As described above, the conventional stent has a problem of not havingboth the flexibility and the radial support force keeping in balance.

As a result of assiduous studies to solve the above-described problemand to provide a stent having both the flexibility and the radialsupport force, the present inventors have reached the present invention.

DISCLOSURE OF THE INVENTION

The present invention is achieved from the point of view describedabove, and according to the present invention, the following inventioncan be provided.

-   [1] A stent 1 (1A, 1B) formed into a generally or substantially    tubular body with annular units composed of a plurality of cells and    being expandable radially outward from inside of the tubular body:

wherein the plurality of the cells 6 (6A, 6B) are connected verticallyand so arranged as to surround the central axis C1 of the stent whichforms the tubular body and thereby to construct annular units 4 (4A,4B);

wherein a plurality of the annular units 4 (4A, 4B) are extended alongthe axis of the stent 1 (1A, 1B) to form the tubular body in such amanner that adjacent annular units 4 (4A, 4B) are connected at least atone portion by a connecting part 5 (5A, 5B); and

wherein each of the cells 6 (6A, 6B) has at least one or more bentportions 12 (12A, 12B), and is formed in such a manner that the angle θof the bent portion after expansion of the tubular body until thediameter becomes at least 2.5 mm is equal to or larger than 30°.

-   [2] The stent 1 (1A, 1B) according to [1], wherein the ratio of the    length 6L (6AL, 6BL) to the length 5L (5AL, 5BL) of the    above-described connecting part in the axial direction of the stent    is formed such that when the length 6L (6AL, 6BL) of the    above-described cells in the axial direction of the stent is assumed    to be 100, then the length 5L (5AL, 5BL) is formed to be 50 to 100.-   [3] The stent 1 (1A, 1B) according to [1] or [2], wherein the    connecting part 5 (5A, 5B) is constructed of at least 2 or more of    bent portions 8 and an approximately or substantially straight line    portion 7 continuing to the bent portions 8, and is connected to the    cells 6 (6A, 6B) constructing adjacent different annular units 4    (4A, 4B) at the ends of the cells.-   [4] The stent 1 (1A) according to any one of [1] to [3], wherein the    cell 6 (6A) is formed by connecting at least one or more    approximately or substantially straight line portions 11 (11A) and    curved line portions 13 (13A) through the bent portion 12 (12A).-   [5] The stent 1B according to any one of [1] to [3], wherein the    cell 6B is formed by connecting an approximately or substantially    straight line portion 11B having an acute angle X with respect to    the center line C2 in the axial direction of each stent 1B to an    approximately or substantially straight line portion 13B disposed    almost horizontally to the center line C2 in the axial direction of    the stent 1B through the above-described bent portion 12B.-   [6] The stent 1 (1A, 1B) according to any one of [1] to-   [5], wherein the connecting part 5 (5A, 5B) is constructed by    connecting the bent portions 8 to the both sides of the central    approximately or substantially straight line portion 7, and the end    portions of the bent portion 8 are connected to the end portions of    the cells 6 (6A, 6B) constructing respective adjacent different    annular units 4 (4A, 4B) through the connection portions 9 (9A, 9B).-   [7] The stent 1 (1A, 1B) according to any one of [1] to-   [6], wherein the cell 6 (6A, 6B) is formed in a vertically    asymmetrical manner to the center line C2, when divided vertically    with the center line C2 in the axial direction of the stent.-   [8] The stent 1 (1A, 1B) according to any one of [1] to-   [7], wherein the connecting parts 5 (5A, 5B) are disposed at least    one or more spaces apart in the radial direction of the stent 1 (1A,    1B).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view showing the stent of the present invention,

FIG. 2 is an enlarged view of FIG. 1.

FIG. 3 is an enlarged view showing a state after expansion of the stentof the present invention,

FIG. 4 is a schematic view of a strut which constructs a cell,

FIG. 5 is an enlarged view when the diameter of the stent is reduced ondelivering to a flood vessel,

FIG. 6 is a plan view showing an example of another embodiment of thestent according to the present invention,

FIG. 7 is a partially enlarged plan view of FIG. 6,

FIG. 8 is a plan view showing an example of yet another embodiment ofthe stent according to the present invention,

FIG. 9 is a partially enlarged plan view of FIG. 8,

FIG. 10 is an enlarged view of a reference example of the stentaccording to the present invention, and

FIGS. 11A, 11B and FIGS. 12A, 12B are plan views of conventional stentsrespectively.

In these drawings, 1, 1A and 1B indicate the stents; 4, 4A and 4Bindicate the annular units; 5, 5A and 5B indicate the connecting parts;6, 6A and 6B indicate the cells; 7 indicates an approximately orsubstantially straight line portion; 8 indicates a bent portion; 9indicates a connection portion; 11, 11A, 11B and 13B indicateapproximately or substantially straight line portions; 12, 12A and 12Bindicate bent portions; 13 and 13A indicate curved line portions; 14 and14A indicate small bent portions; 15 indicates an approximately orsubstantially straight line portion; 17 indicates an approximately orsubstantially<shaped cell; 18 indicates an approximately orsubstantially S-shaped connecting part; and 19 indicates a unit part ofthe construction in the stents A, B.

Preferred Embodiments of the Invention

The present invention will be explained below in detail referring to thedrawings.

FIG. 1 is a plan view showing a stent of the present invention, FIG, 2is an enlarged view of FIG. 1, FIG. 3 is an enlarged view showing astate after expansion of the stent of the present invention, and FIG. 4is a schematic view of a strut which constructs a cell.

The stent 1 is, as shown in FIG. 1, formed into a generally orsubstantially tubular body from annular units 4 consisting of aplurality of cells 6, and is expandable radially outward from inside ofthe tubular body wherein a plurality of the cells 6 are connectedvertically and so arranged to surround the central axis C1 of the stent1 and thereby forming the annular units 4. A plurality of the annularunits 4 are extended along the axis of the stent 1 which forms thetubular body in a manner that adjacent annular units 4 are connected atleast at one portion by a connecting part 5.

In the present invention, the cell 6 means one of constitutional unitsof patterns consisting the surface of the stent 1 and, as shown in FIG.2, it includes all forms having at least one or more of bent portions12, more concretely, bent portions 12 with acute angles X, and beingconstructed by connecting approximately or substantially straight lineportions 11 and curved line portions 13 through the bent portion 12. Inaddition, when each of the cells 6 is divided vertically by the centerline C2 in the axial direction of the stent, the cells 6 are formed in avertically asymmetrical manner to the center line C2 so that the angle θof the bent portion 12 after expansion of the tubular body is 30° ormore as shown in FIG. 3, when, for example, the diameter φ of thetubular body, namely of the stent, is expanded to 2.5 mm.

Incidentally, the angle θ of the bent portion 12 after expansion means,as shown in FIG. 3, an angle formed at the point 0 on the bent portion12 between the approximately or substantially straight line portion 11and an approximately or substantially straight line portion 15 which isnear the point O side of the curved line portion 13.

The cell 6 is constructed by connecting the approximately orsubstantially straight line portion 11 and the curved line portion 13through the bent portion 12 as shown in FIG. 2, and it is preferablethat the curved line portion 13 is constructed by forming two or moresmall bent portions 14 with an obtuse angle Y.

When the approximately or substantially straight line portion 11, thebent portion 12 and the curved line portion 13 having small bentportions 14, all of which constitute the cell 6 (hereinafter alsoreferred to as an approximately or substantially S-shaped portion) standmore perpendicularly with respect to the central axis C1 of the stent(or the tubular body) after expansion of the stent, the radial supportforce of the stent becomes larger. That is, as shown in FIG. 3, thecloser to 180° the angle θ of the bent portion 12 after expansionreaches, the larger the radial support force of the stent becomes.Therefore, when designing the stent, it is preferable to design in sucha manner that the angle θ of the bent portion 12 after expansion of thetubular body reaches at least 30° or more when the diameter φ of thetubular body becomes at least up to 2.5 mm, more preferably up to 3.0mm.

Additionally, since these are related to the number of arrangement ofthe cells 6, the number of radial disposition of the cells 6 ispreferably 4 or more. Furthermore, when the diameter φ of the tubularbody or the stent after expansion is 3.0 mm or more, it is desirable todispose the cells at least 6 pieces or more, preferably 6 pieces to 12pieces.

In the axial direction of the stent, it is desirable to dispose 3 piecesor more, more preferably, 4 pieces to 8 pieces per 10 mm of the lengthin the axial direction of the stent, and when the diameter of the stentreaches the diameter on target for the stent expansion (spec diameter,for example, φ=3.0 mm or φ=4.0 mm), it is desirable, for example, todesign the angle θ of the bent portion 12 after expansion to be at least30° or more, preferably between 45° and 140°, more preferably between45° and 120° as described previously.

It should be noted that, as for the diameter on target (targeteddiameter), it is effective for the better radial support force of thestent to design the angle θ after expansion to be near 180°, forexample, over 140°, as described above. However, it is not favorablebecause of the following problems such that the amount of deformation ofthe bent portion 12 becomes too large to maintain the strength of it ina favorable state, and the reduction in total length of the stentaccompanied by the expansion (hereinafter referred to as foreshortening)becomes too large to make an easy positioning of the stent whendetaining the stent.

It is preferable for the shape of the strut of the cell 6 to formasymmetrically with respect to the center line C2 of respective cells inthe axial direction of the stent as shown in FIG. 4 b, rather than toform symmetrically as shown in FIG. 4 a. This is because thatasymmetrical formation of the strut makes the relative length of thewhole strut longer (for instance, when FIG. 4 a is compared with FIG. 4b, it is always found to be 2 a<c+d), enhances the expandability of thestent itself, and enhances the suppression effect of the foreshortening.

The connecting part 5 between cell 6 and 6 in the stent 1 is constructedby having at least two or more of bent portions and by connecting thebent portions 8 and 8 to both sides of the central approximately orsubstantially straight line portion 7, and the end portions of the bentportions 8 are connected to the end portions of the cells 6 and 6 whichconstruct respectively different (adjacent) annular units 4 and 4through the connection portions 9 and 9, as shown in FIG. 2.

Incidentally, the connecting part 5 is connected to both sides of thecells 6 and 6 in a bilaterally asymmetrical manner, as shown in FIG. 2.

As for the length of the connecting part 5, it is preferable for thetotal length of the approximately or substantially straight line portion7 and the bent portions 8 and 8 to be 1 mm or more because theflexibility of the stent is believed that the longer the total length ofthe stent the more the flexibility is improved. However, if it is toolong, the connecting part 5 in an approximately or substantially S shapebecomes proportionally large, which makes vertically adjacent connectingparts 5 interfere in each other, thereby conversely spoiling theflexibility, when the stent is mounted on a balloon catheter (thediameter of the stent may be sometimes reduced a little on the ballooncatheter), or when the stent is bent along the blood vessel duringpassing through the bent portion of the blood vessel. Therefore, it ispreferable for the total length of the connecting part to be 1 mm ormore, preferably 1 mm to 2 mm. It is further desirable for R (radius) ofan arc constructing the bent portion 8 to be 0.05 mm or more, preferably0.05 mm to 0.2 mm because of the above reason.

Further, in the present invention, as shown in FIG. 2, with the ratio ofthe length 6L to the length 5L, it is preferable for the length 5L ofthe connecting part 5 in the axial direction of the stent to be 50 to100 on the basis that the length 6L of the cells 6 in the axialdirection of the stent is assumed to be 100. For convenience of design,it is more preferable to form in the length of 50 to 90. Thereby, theflare phenomenon after expansion of the stent or during delivery can besuppressed and at the same time, flexibility can be given to the stentitself.

The characteristics of the pattern of the stent 1 according to thepresent invention is as follows:

For example, as shown in FIG. 2, the cells 6 are disposed or placedrespectively asymmetrically with respect to the center line C2 in theaxial direction of the stent through the connecting part 5. However, inthe axial direction of the stent, they are disposed in the samedirection and at the same height. In other words, the cells 6 in theaxial direction of the stent are disposed so as to align and lie on topof one another if the cells 6 are shifted in the axial direction of thestent from the nth line (column) to the (n+1)th line (column), and thecells 6 in the same line (the same annular unit) are disposed in thesame direction in the radial direction of the stent so as to align andlie on top of one another if they are slid vertically from their presentpositions to upward or downward in the same line. Incidentally, thoughapproximately or substantially straight line portion 11 of each cell isin substantially horizontal (substantially in parallel) to the centerline C2 respectively, it may be inclined at some angles in a range notto be less than 30° of the angle θ of the bent portion 12 afterexpansion.

Further, though the connecting parts 5 are also disposed asymmetricallyin the axial direction of the stent through the cell 6, they aredisposed facing in the same direction in the axial direction of thestent and at the same height. In other words, the connecting parts 5 inthe axial direction of the stent are seen to be disposed so as to alignand lie on top of one another if the connecting parts 5 are shifted inthe axial direction of the stent from the nth line to the (n+1)th line,and the connecting parts in the same line are seen to be disposed in thesame direction in the radial direction of the stent so as to align andlie on top of one another if they are slid vertically from their presentpositions to upward or downward of the same line.

In the stent of the present invention, the width of the strutconstructing the cell 6 is preferably wider than the width of the strutconstructing the connecting part 5, and the heights of the cell 6 andthe connecting part 5 in the axial direction of the stent are preferablydisposed in such a manner that both are shifted to each other so as tobe at a different height from each other, not to be at the same height.

As described above, in the stent 1 of the present invention, byspecifying the angle θ of the bent portion 12 after expansion, the ratioof the length 6L in the axial direction of the stent of the cell 6 tothe length 5L in the axial direction of the stent of the connectingpart, the shape and size of the connecting part 5 and the cell 6, thedisposition (pattern) in the radial direction and the axial direction ofthe stent of the connecting part 5 and the cell 6 as above, the cells 6and the connecting parts 5 do not align and do not lie respectively ontop of one another three-dimensionally in the radial direction of thestent when the diameter of the stent 1 is reduced during delivering tothe blood vessel as shown in FIG. 5. That is, when the diameter of thestent 1 is reduced as shown in FIG. 5, they are formed to fit in thespace S in the radial direction of the stent existing between each ofthe cells 6 and the connecting parts 5 as shown in FIG. 2.

FIG. 6 and FIG. 8 are plan views showing examples of other embodimentsof the present invention and FIG. 7 and FIG. 9 are partially enlargedplan views of FIG. 6 and FIG. 8 respectively.

The stent 1A shown in FIG. 6 and FIG. 7 is basically the same exceptingonly the following point when compared with the stent 1 shown in FIG. 1.That is, (a) each of the cells 6A is constructed by connectingapproximately or substantially straight line portion 11A having an acuteangle X with respect to respective center line C2 in the axial directionof the stent 1A to the curved line portion 13A through the bent portion12A (while the stent 1 is constructed by connecting approximately orsubstantially straight line portion 11 disposed almost horizontally(substantially in parallel) with respect to respective center line C2 inthe axial direction of the stent 1 to the curved line portion 13 throughthe bent portion 12), (b) the cells 6A are disposed in a bilaterallysymmetrical manner in the axial direction of the stent 1A through theconnecting part 5A, (c) the cells 6A in the axial direction of the stent1A are disposed to align and lie on top of one another when seen fromthe cells in the nth line to the cells in the (n+2)th line, on everyother line in the axial direction of the stent 1A. Since respectiveother construction members and the definitions thereof are substantiallythe same as those in the stent 1, the detailed explanation thereof willbe omitted here.

Furthermore, the stent 1B shown in FIG. 8 and FIG. 9 is different fromthe stents 1 and 1A shown in FIG. 1, FIG. 6 and FIG. 7 only in the pointthat (a) each of the cells 6B is constructed by connecting anapproximately or substantially straight line portion 11B having an acuteangle X with respect to respective center lines C2 in the axialdirection of the stent 1B to an approximately or substantially straightline portion 13B disposed almost horizontally (substantially inparallel) with the center line C2 in the axial direction of the stent 1through the bent portion 12B (while in the stent 1, and stent 1A, eachof the cells 6 and 6A is constructed by connecting the approximately orsubstantially straight line portion 11, 11A to the curved line portion13, 13A through the bent portion 12). Though the following points of (b)respective cells 6B are disposed in a bilaterally symmetrical manner inthe axial direction of the stent 1B through the connecting part 5B, and(c) the cells 6B in the axial direction of the stent 1B are disposed toalign and lie on top of one another when seen in the axial direction ofthe stent 1B from the cells in the nth line to those in the (n+2)thline, on every other line in the axial direction of the stent 1B aredifferent from the stent 1, the stent 1B is substantially the same withthe points of (b) and (c) as those in the stent 1A. Since respectiveother construction members and the definitions thereof are substantiallythe same as those in the stent 1 and the stent 1A, the detailedexplanation thereof will be omitted here.

In the stents 1, 1A and 1B shown in the above-described FIG. 1, FIG. 6and FIG. 8 of the present invention, though the connecting parts 5, 5Aand 5B of the cells 6, 6A and 6B constructing respective annular units4, 4A and 4B are disposed continuously without space in the radialdirection of the stents 1, 1A and 1B, they may be disposed with at leastone or more spaces in the radial direction. Thus, by disposing theconnecting parts suitably with one space apart or one or two spacesapart, the whole stents 1, 1A, 1B become more flexible so that thedeliverability to branched blood vessels is expected to improve.

As a material constructing the stents 1, 1A, 1B of the presentinvention, well-known materials itself can be used without anylimitation and a metal pipe made of, for example, stainless steel suchas SUS 316L and the like, a shape memory alloy such as Ti—Ni alloy,Cu—Al—Mn alloy and so on, Cu—Zn alloy, Ni—Al alloy, titan, titan alloy,tantalum, tantalum alloy, platinum, platinum alloy, tungsten andtungsten alloy is used to form the stent by a laser processing method orother processing method.

On the surface of the stent formed with these metals, a polymericmaterial having compatibility with a living body such as polyurethane,polyvinyl pyrrolidine, or polyvinyl alcohol, or a material in which theabove polymeric material is fixed with a physiologically activesubstance such as heparin, urokinase and the like by chemical bonding,and a material in which the above polymeric material is mixed with anantithrombosis medicine such as argatroban, cilostazol, sarpogrelateHCl, and so on may be applied as a coating.

EXAMPLE 1

In the stent A (B) constructed by unit parts 19 of the constructionconsisting of approximately or substantially<shaped cells 17 andapproximately or substantially S-shaped connecting parts 18, as shown inFIG. 10, in order to evaluate difference in radial support force due tothe difference of the angle after expansion, the stent A (the number ofarrangement: 8) and the stent B (the number of arrangement: 6) which aredifferent in the number of arrangement of the unit parts 19 of theconstruction in the circumferential direction, are prepared as below,and respective radial support forces are evaluated and compared.

stent A: the number of the unit parts 19 to be arranged 8 strut width ofthe cell 17 0.12 mm 1 θ angle after expansion by 3 mm 60° stent B: thenumber of the unit parts 19 to be arranged 6 strut width of the cell 170.12 mm 1 θ angle after expansion by 3 mm 81°

The evaluation is carried out by expanding respective stents in asilicone tube disposed in a chamber by 3 mm of the diameter φ. Afterdetaining them, change in the outer diameter of the stents whileapplying pressure in the chamber with air is measured to evaluate. Themeasurement result is shown in Table 1.

TABLE 1 (measurement result of the radial support force) stent A stent Bamount of change in the −0.07 mm −0.04 mm outer diameter when applyingpressure of 0.02 MPa

As clearly shown in Table 1, while the amount of change in the outerdiameter is −0.04 mm (which means the outer diameter is shortened by0.04 mm) in the stent B having a larger angle (1θ) after expansion, theamount of change in the outer diameter is −0.07 mm (which means theouter diameter is shortened by 0.07 mm) in the stent A. Thus, it wasconfirmed that the stent B is smaller in the amount of change in theouter diameter and larger in the radial support force.

EXAMPLE 2

The stent 1 shown in FIG. 1 was prepared, and the radial support forcewas compared with conventional stents 201 (FIG. 11) and 241 (FIG. 12)and the flexibility was compared with the stent 201 to evaluate. Theevaluation of the radial support force was carried out in the samemanner as in the example 1, and the flexibility was evaluated by the 4point bending test. The measurement result of the radial support forceis shown in Table 2 and the measurement result of the flexibility isshown in Table 3.

TABLE 2 (measurement result of the radial support force) stent 1 stent201 stent 241 amount of change in the −0.026 mm −0.05 mm −0.030 mm outerdiameter when applying pressure of 0.02 MPa

TABLE 3 (measurement result of the flexibility) stent 1 stent 201flexural strength 11.7N · mm 17.1N · mm

As clearly shown in Table 2, it is recognized that the amount of changein the outer diameter of the stent 1 of the present invention is smallerthan those of both the stent 201 and the stent 241, and, as is clearfrom the result in Table 3, the flexural strength is smaller than thatof the stent 201. As described above, the stent 1 of the presentinvention is recognized to be a stent having both a high radial supportforce and high flexibility.

EXAMPLE 3

The radial support force and the flexibility of the stent 1A shown inFIG. 6 (FIG. 7) and the stent 1B shown in FIG. 8 (FIG. 9) were measuredand evaluated in the same manner as in Example 1 and Example 2. Themeasurement result of the radial support force is shown in Table 4 andthe measurement result of the flexibility is shown in Table 5. As isclear from Tables, it is recognized that substantially the same resultsas in the stent 1 are obtained also as for the stent 1A and the stent1B.

TABLE 4 (measurement result of the radial support force stent 1A stent1B stent 201 stent 241 amount of change −0.033 mm −0.031 mm −0.05 mm−0.030 mm in the outer diameter when applying pressure of 0.02 MPa

TABLE 5 (measurement result of the flexibility) stent 1A stent 1B stent201 flexural 13.7N · mm 14.3N · mm 17.1N · mm strength

EXAMPLE 4

As for the stents 1, 1A, 1B in the present invention, the foreshorteningvalues when the diameter φ of the stents were expanded to 3.0 mm weremeasured. The measurement was carried out in such a manner that eachstent length (referred to as L1) before expansion and the correspondingstent length (referred to as L2) after expansion to 3.0 mmφ weremeasured and the reduction ratios of the total length were calculatedwith the following formula to have the foreshortening value.Foreshortening value=((L1−L2)/L1)×100

As comparison examples, the same measurements were made for the stent201 and the stent 241. The result is shown in Table 6.

TABLE 6 stent 1 stent 1A stent 1B stent 201 stent 241 foreshortening1.5% 1.5% 3% 5.6% 5.6% value

As is clear from Table 6, the foreshortening values of all stents 1, 1Aand 1B of the present invention are recognized to be far smaller thanthose of the conventional stents 201 and 241.

INDUSTRIAL UTILITY

The stent of the present invention can ensure sufficiently both of highflexibility and a high radial support force and at the same time enhancethe expandability of the blood vessel and suppress the foreshorteningand the flare phenomenon, so that it can be preferably used as a stentto expand a narrowed portion of the blood vessel to ensure a necessaryand important tubular region.

What is claimed is:
 1. A stent formed into a generally or substantially tubular body comprising: annular units composed of a plurality of cells, said annular units radially expandable outward from inside of the tubular body, wherein the plurality of the cells of each annular unit are connected vertically and arranged surrounding a central axis of the stent; wherein said annular units are disposed along an axial direction of said stent, and adjacent annular units are connected at least at one portion by a connecting part; said connecting part being a generally S-shaped connecting part, said S-shaped connecting part including two or more arcs and a substantially straight line portion between two arcs, each free end of the arcs extending substantially upward or downward as high as about a middle of said straight line portion thereby forming a full fledged S-shaped connecting part, and ends of said connecting part are respectively connected to a left portion and a right portion of cells forming adjacent annular units respectively; each cell being composed of two struts, a first substantially straight strut being disposed in the axial direction as a base strut (BS-strut), and a second curved strut disposed at an acute angle X with respect to the axial direction of the stent as a bending strut (BN-strut), and said acute angle X being substantially maintained between a major or majority part of said first straight strut (BS-strut) and a major or majority part of the second curved strut (BN-strut) thereby the majority part of the base strut (BS-strut) and the majority part of the bending strut (BN-strut) are substantially not in parallel with each other, wherein a substantially straight line portion forming a part of said second curved strut (BN-strut) is connected to the first substantially straight strut (BS-strut) via a bent portion, thereby the stent is configured to be compressed such that said first straight strut composing the base strut remains in the axial direction, and said second curved strut composing the bending strut bends toward the base strut, and said stent being expandable to at least a diameter of 2.5 mm when an angle formed between said first strut and said substantially straight line portion of the second strut is 30°–140°.
 2. The stent according to claim 1, wherein a ratio of a length of said cell in the axial direction of the stent to a length of said connecting part in the axial direction of the stent is such that when the length of said cell in the axial direction of the stent is 100, the length of said connecting part in the axial direction of the stent is 50 to
 100. 3. The stent according to claim 2, wherein said cells are all equal in size.
 4. The stent according to claim 2, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 5. The stent according to claim 4, wherein said cells are all equal in size.
 6. The stent according to claim 2, wherein said connecting parts are configured to be disposed at intervals of at least one connecting part, putting at least one or more spaces therebetween without disposing the connecting parts continuously and spacelessly in a radial direction of the stent.
 7. The stent according to claim 6, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 8. The stent according to claim 7, wherein said cells are all equal in size.
 9. The stent according to claim 6, wherein said cells are all equal in size.
 10. The stent according to claim 1, wherein said connecting parts are configured to be disposed at intervals of at least one connecting part, putting at least one or more spaces therebetween without disposing the connecting parts continuously and spacelessly in a radial direction of the stent.
 11. The stent according to claim 10, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 12. The stent according to claim 10, wherein said cells are all equal in size.
 13. The stent according to claim 11, wherein said cells are all equal in size.
 14. The stent according to claim 1, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 15. The stent according to claim 14, wherein said cells are all equal in size.
 16. The stent according to claim 1, wherein said cells are all equal in size.
 17. A stent formed into a generally or substantially tubular body comprising: annular units composed of a plurality of cells, said annular units radially expandable outward from inside of the tubular body, wherein the plurality of the cells of each annular unit are connected vertically and arranged surrounding a central axis of the stent; wherein said annular units are disposed along an axial direction of said stent, and adjacent annular units are connected at least at one portion by a connecting part; said connecting part being a generally S-shaped connecting part, said S-shaped connecting part including two or more arcs and a substantially straight line portion between two arcs, each free end of the arcs extending substantially upward or downward as high as about a middle of said straight line portion thereby forming a full fledged S-shaped connecting part, and ends of said connecting part are respectively connected to a left portion and a right portion of cells forming adjacent annular units respectively; each cell being composed of two struts, a first curved strut being disposed in the axial direction as a base strut (BS-strut), and a second substantially straight strut disposed at an acute angle X with respect to the axial direction of the stent as a bending strut (BN-strut), and said acute angle X being substantially maintained between a major or majority part of said first curved strut (BS-strut) and a major or majority part of the second substantially straight strut (BN-strut) thereby the majority part of the base strut (BS-strut) and the majority part of the bending strut (BN-strut) are substantially not in parallel with each other, wherein a substantially straight line portion forming a part of said first curved strut (BS-strut) is connected to the second substantially straight strut (BN-strut) via a bent portion, thereby the stent is configured to be compressed such that said first curved strut composing the base strut remains in the axial direction, and said second straight strut composing the bending strut bends toward the base strut, and said stent being expandable to at least a diameter of 2.5 mm when an angle formed between said substantially straight line portion of said first curved strut and the second substantially straight strut is 30°–140°.
 18. The stent according to claim 17, wherein a ratio of a length of said cell in the axial direction of the stent to a length of said connecting part in the axial direction of the stent is such that when the length of said cell in the axial direction of the stent is 100, then the length of said connecting part in the axial direction of the stent is 50 to
 100. 19. The stent according to claim 18, wherein said cells are all equal in size.
 20. The stent according to claim 18, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 21. The stent according to claim 20, wherein said cells are all equal in size.
 22. The stent according to claim 18, wherein said connecting parts are configured to be disposed at intervals of at least one connecting part, putting at least one or more spaces therebetween without disposing the connecting parts continuously and spacelessly in a radial direction of the stent.
 23. The stent according to claim 22, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 24. The stent according to claim 23, wherein said cells are all equal in size.
 25. The stent according to claim 22, wherein said cells are all equal in size.
 26. The stent according to claim 17, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 27. The stent according to claim 26, wherein said cells are all equal in size.
 28. The stent according to claim 17, wherein said cells are all equal in size.
 29. The stent according to claim 17, wherein said connecting parts are configured to be disposed at intervals of at least one connecting part, putting at least one or more spaces therebetween without disposing the connecting parts continuously and spacelessly in a radial direction of the stent.
 30. The stent according to claim 29, wherein said cells are all equal in size.
 31. The stent according to claim 29, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 32. The stent according to claim 31, wherein said cells are all equal in size.
 33. A stent formed into a generally or substantially tubular body comprising: annular units composed of a plurality of cells, said annular units radially expandable outward from inside of the tubular body, wherein the plurality of the cells of each annular unit are connected vertically and arranged surrounding a central axis of the stent; wherein said annular units are disposed along an axial direction of said stent, and adjacent annular units are connected at least at one portion by a connecting part; said connecting part being a generally S-shaped connecting part, said S-shaped connecting part including two or more arcs and a substantially straight line portion between two arcs, each free end of the arcs extending substantially upward or downward as high as about a middle of said straight line portion thereby forming a full fledged S-shaped connecting part, and ends of said connecting part are respectively connected to a left portion and a right portion of cells forming adjacent annular units respectively; each cell being composed of two struts, wherein one strut of the two being substantially straight strut and an other being a curved strut, and wherein one strut of the two being disposed in the axial direction as a base strut (BS-strut), and the other strut disposed at an acute angle X with respect to the axial direction of the stent as a bending strut (BN-strut), and said acute angle X being substantially maintained between a major or majority part of said first base strut and a major or majority part of second bending strut, thereby the majority part of the base strut (BS-strut) and the majority part of the bending strut (BN-strut) are substantially not in parallel with each other, wherein said two struts are connected via a bent portion, the stent is configured to be compressed such that said first strut composing the base strut remains in the axial direction, and said second strut composing the bending strut bends toward the base strut, and said stent being expandable to at least a diameter of 2.5 mm when an angle formed between said two struts is 30 °–140°.
 34. The stent according to claim 33, wherein said cells are all equal in size.
 35. The stent according to claim 33, wherein a ratio of a length of said cell in the axial direction of the stent to a length of said connecting part in the axial direction of the stent is such that when the length of said cell in the axial direction of the stent is 100, the length of said connecting part in the axial direction of the stent is 50 to
 100. 36. The stent according to claim 35, wherein said cells are all equal in size.
 37. The stent according to claim 35, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 38. The stent according to claim 37, wherein said cells are all equal in size.
 39. The stent according to claim 35, wherein said connecting parts are configured to be disposed at intervals of at least one connecting part, puffing at least one or more spaces therebetween without disposing the connecting parts continuously and spacelessly in a radial direction of the stent.
 40. The stent according to claim 39, wherein said cells are all equal in size.
 41. The stent according to claim 39, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 42. The stent according to claim 41, wherein said cells are all equal in size.
 43. The stent according to claim 33, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 44. The stent according to claim 43, wherein said cells are all equal in size.
 45. The stent according to claim 33, wherein said connecting parts are configured to be disposed at intervals of at least one connecting part, putting at least one or more spaces therebetween without disposing the connecting parts continuously and spacelessly in a radial direction of the stent.
 46. The stent according to claim 45, wherein said cells are all equal in size.
 47. The stent according to claim 45, wherein said cells are bilaterally symmetric in the axial direction of the stent through the connecting parts.
 48. The stent according to claim 47, wherein said cells are all equal in size. 